Elastomeric yarns consist of single or multiple elastomeric fibers that are manufactured in fiber-spinning processes. By “elastomeric fiber” is meant a continuous filament which, free of diluents, has a break elongation in excess of 100% independent of any crimp, and which, when stretched to twice its length, held for one minute, and then released, retracts to less than 1.5 times its original length within one minute of being released. Such elastomeric fibers are formed from polymers including, but not limited to, rubber, spandex, polyetherester, and elastoester. Elastomeric fibers differ from “elastic fibers” or “stretch fibers,” which have been treated in such a manner as to have the capacity to elongate and contract. “Elastic fibers” or “stretch fibers” have modest power in contraction, and include, but are not necessarily limited to, fibers formed by false-twist texturing, crimping, etc.
Elastomeric yarns can be formed with elastomeric fibers produced from fiber-spinning processes, such as dry spinning, wet spinning, or melt spinning. In particular, dry spinning is the process of forcing a polymer solution through spinneret orifices into a chamber to form a filament or filaments. Heated inert gas is passed through the chamber, evaporating the solvent from a filament as the filament passes through the chamber. Multiple filaments are coalesced together while passing through the chamber, thereby forming an elastomeric yarn.
As shown in FIGS. 1 to 7 (Prior Art), continuous-filament elastomeric single filaments or yarns produced by any of these spinning technologies generally are wound onto individual cylindrical tube cores 10 to form supply packages 20 of required size and weight. Package dimensions and weight depend, for example, on the yarn denier, the end-use requirements of the yarn, and the winding equipment employed in the process. The yarn length 12 wound around a core 10 to form a package 20 has a proximal or beginning end 14 and a distal or terminal end 18. The beginning end 14 is located on or adjacent to the outer circumferential surface of the tube core 10, which core 10 supports the inside diameter of the wound yarn package 20. This beginning end 14 is also called a “transfer tail.”
The transfer tail 14 preferably is located on the tube core 10 in a position outside the body of the package 20 as illustrated in FIG. 5. To begin winding a yarn package 20, the transfer tail 14 is formed by winding a number of wraps of yarn in a single location along the tube core 10 to form a bunch on the tube core. This bunch holds the transfer tail 14 in place. Then, the yarn 12 is wound or coiled over the tube core 10 in a yarn-traverse motion to form the yarn package 20.
Although the transfer tail 14 is preferably located outside the body of the package 20, as described above, it is more usually trapped under the yarn windings in the yarn package as illustrated in FIG. 3. This is normally the result of equipment or process limitations. When the yarn package has a desired diameter, the yarn is broken by the action of the winding equipment to leave a terminal or distal end 18. The terminal end 18 of the yarn length is located on the outside-diameter surface of the yarn package (FIGS. 3 and 4).
All individually wound packages of elastomeric yarns must be unwound for use in subsequent processes, such as, for example, covering, knitting, and weaving. Currently, packages of elastomeric yarn are unwound by beginning at the outside of the yarn package and pulling the yarn from its terminal or distal end 18. This method of unwinding will be designated herein as “outside in” because the yarn package 20 is unwound continuously from the outside until reaching the outer circumferential surface of the tube core 10 and the distal or beginning end 14 (transfer tail) of the yarn length.
To continuously unwind multiple packages of elastomeric yarn for uninterrupted delivery to subsequent processes, one must be able to fix or tie an end of a yarn length from a first package to an end of a yarn length from a second package, and so on. Generally, the transfer tail of the first package is tied to the terminal or distal end of the second package. One method for continuous unwinding of yarn from multiple yarn packages is called “overend outside-in unwinding” and is shown schematically in FIG. 7. With such unwinding method, the yarn is pulled away from the package in a direction along the axis of the tubular core and is unwound over the end of the package. In the example shown in FIG. 7, the tube cores 10a, 10b and 10c of three yarn packages 20a, 20b and 20c, are loaded onto spools 24a, 24b and 24c. Before the unwinding begins, the transfer tail 14a is tied by knot 13a to the beginning end 12b of the second yarn package 20b, and the transfer tail 14b of the second yarn package 20b is tied by knot 13b to the beginning end 12c of the third yarn package 20c. The yarn 12a from first yarn package 20a is unwound from the outside in. After all yarn has been unwound from the first yarn package 20a, the unwinding process continues by next unwinding yarn from the second yarn package 20b, and so on.
Continuous unwinding processes where elastomeric yarns are unwound from the outside-in have encountered problems. If the transfer tail of a package is trapped, it is generally not possible or practical to retrieve the trapped end for tying it together to the beginning end of a next yarn package. The yarn tension necessary to unwind the yarn in an overend outside-in method is related to factors such as the yarn takeoff speed, the denier of the yarn, the dimensions of the package and the tackiness of the yarn surface, to name some important variables. For elastomeric yarns, it is desirable and necessary to keep the pulling tension low and minimize variations in that tension during unwinding, because elastomeric yarns have a low modulus of elasticity and are very sensitive to tension. Variable yarn elongation during unwinding can affect subsequent product quality. Furthermore, when the unwinding yarn is transferred to another package by means of a transfer tail tied to the beginning end of the next package, there is normally a sharp increase in yarn tension for a very short time interval—i.e., a tension spike. This tension spike occurs while unwinding the last few wraps of the yarn on the tube core. The spike affects unwound-yarn quality and can also cause the yarn to break, which is an expensive interruption to the process.
As mentioned above, the unwinding tension is related to the tackiness of the yarn, or the tendency for the yarn to stick to itself and to other materials. All elastomeric yarns, as spun and without special chemical additives or surface finishes, have some degree of surface tackiness. This tackiness is especially evident with wound packages of dry-spun spandex, where the compressive pressure on underlying yarns can be very high due to the stretch and tension of the yarn as it is being spun and wound, which is a natural requirement of the process. The compressive pressure is greatest on the yarn wound near the core of the package. This can make it especially difficult to unwind and use yarn wound near the core of the package, where conditions are most extreme. In addition, time and temperature contribute to tackiness, so that packages of spandex that have been stored, for example for months, are more difficult to unwind and experience significantly more core waste than freshly spun and wound packages.
Reducing the tackiness and the resulting waste would improve the economics of spandex yarn and filament production. For some spandex-yarn applications, however, methods to reduce tackiness are not acceptable because the yarns will be made into garments using adhesives that must adhere effectively to the elastomer yarn surface. Moreover, even if a transfer tail is available, continuous unwinding of multiple packages of high tack yarns generally has not been practical because the severe tension spike during package transfer will often break the yarn. Especially for tacky elastomeric yarns, new methods of unwinding with reduced and more uniform yarn tensions are needed for improved process continuity and product quality.